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Odorant binding protein

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1 Introduction
2 OBP in insects
3 See also
4 References

Introduction

Odorant-binding protein (OBP) are soluble proteins which involve in the processes of odorant detection in the olfactory sensilla.

The first OBP that was identified is Bovine odorant binding protein, that was isolated from a cow's mucus ref. Though functunaly same, vertebrates and insects OBP are stucture and different.

OBPs are important for insect olfaction. For instance, OBP76a (LUSH) in the fly Drosophila melanogaster is required for the detection of the pheromone vaccenyl acetate [Ha and Smith, 2006; Xu et al., 2005] and has been proven to adopt a conformation that activates the odorant receptor [Laughlin et al., 2008].

Bombykol, a sex pheromone of Bombyx mori, from PubChem

OBP in insects

OBP Function

Despite three decades of intensive research, the exact roles of OBP and the mechanism by which the odorant receptor (OR) is activated are still in dispute ^[1]^[2]. Of all, the role of OBP as an odorant carrier is generally accepted.

A few functions have been suggested for OBP: 1. 2. 3. 4.

In order to explain the structure and function of these fascinating proteins, this page will further focus on a particular OBP - the well investigated Bombyx mori PBP: BmorPBP.

PBP

PBPs are specialized members of the insect odorant-binding protein (OBP) super-family, and they are devided into three groups by their lengths: long-chain PBPs (∼160 aa), medium-chain PBPs (∼120 aa), and short-chain PBPs (∼110 aa) ^[3]

Bombyx mori BmorPBP (lets talk about sex..)

1 BmorPBP structure and function
- 1.1 BmorPBP ligand and ligand binding
- 1.2 Protein conformations
2 Receptor activation

BmorPBP structure and function

This protein was first identified in the B. mori male antennae by Krieger et al. in 1996 ^[4] . It has 164 amino acids that forms 6-7 alpha helices. Three 3 disulfide bonds formed by 6 cystein residues tied four helices. As expected from a soluble protein, its surface is covered with charged residues.

BmorPBP ligand and ligand binding

The protein natural ligand is the moth pheromone bombykol. However, it was demonstrated that other molecules can also bound to the protein cavity ^[5]. The interaction with the ligand is beeing made by 4 alpha helices in the core of the protein, which form the binding cavity ^[6]. The hydroxyl group of the pheromone bombykol forms a hydrogen bond with the sidechain of Ser56 (O–O distance of 2.8 Å).

Protein conformations

The PBP has two pH-dependent conformations, with different ligand affinities: the "open form" (A) and the "close form" (B) ^[7]. The pheromone bombykol, and the seventh α-helix loacated in the C terminus of the protein compete for the binding site. In a nuetral pH (6.5-7) the protein is in the "open form" (A), in which the

The C terminus of the protein bears mostly nonpolar amino acids. Yet on the surface of the helix there are three exceptional amino acids: Asp-132, Glu-137, and Glu-141, which are conserved in moth PBP ^[8].

. Of these, residues Asp-132 and Glu-141 form a molecular switch, which upon protonation at low pH triggers the formation of the C-terminal α-helix (101).

The pH dependent theory

According to this theory,

Receptor activation

The surface of the dendrite is negatively charged ^[9], which cause the accumulation of positively charged kations near the membrane surface (20-50 nm), thereby inducing a low pH environment near the dendrite membrane kaissling 2009

Leal WS, et al. (2005) Kinetics and molecular properties of pheromone binding and release. Proc Natl Acad Sci USA 102(15):5386–5391.

The other theory

The BPB ligand is the moth pheromone

References

Proteopedia Page Contributors and Editors (what is this?)

Nurit Eliash, Michal Harel, Joel L. Sussman, Alexander Berchansky, Jaime Prilusky

Retrieved from "http://52.214.119.220/wiki/index.php/Odorant_binding_protein"

Odorant binding protein

From Proteopedia

Contents

Introduction

OBP in insects

OBP Function

PBP

Bombyx mori BmorPBP (lets talk about sex..)

Contents

BmorPBP structure and function

BmorPBP ligand and ligand binding

Protein conformations

Receptor activation

See also

References

Proteopedia Page Contributors and Editors (what is this?)

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